The present invention concerns a manufacturing method for a plurality of photovoltaic cells and more particularly a method for the batch manufacture of a plurality of such cells.
Photovoltaic cells, more commonly designated solar cells, are semi-conductor junction devices which convert luminous energy into electric power. The typical structure of a photovoltaic cell essentially includes five layers, namely a first and second electrode, and a composite body of semi-conductor material which is inserted between the two electrodes and which includes three superposed layers forming an n-i-p or p-i-n junction. One of the two electrodes is transparent to light. When the light reaches the layers forming the photovoltaic semi-conductor body, the device generates a voltage across the electrodes which increases with the increase in light intensity.
These solar cells are widely used in consumer products such as watches or electronic calculators, as well as in industrial products for the generation of electric power from solar energy.
The industrial scale batch manufacture of this type of cell is relatively recent and has for a long time been limited by the absence of appropriate cell manufacturing techniques. Manufacturing techniques have however recently been developed for making reliable photovoltaic cells on an industrial scale at a low cost.
U.S. Pat. No. 4,485,125 discloses such a method for continuously manufacturing a plurality of solar cells on an elongated web of substrate material. According to this method, layers of semi-conductor materials forming at least one n-i-p or p-i-n junction of very high quality are continuously deposited by plasma on a flexible substrate extending from a pay off reel to a take up reel. The product obtained by such a method typically includes a web or strip of conductive material forming the substrate and lower electrode, this strip being coated with three successive respectively n-i-p layers of semi-conductor materials and a layer of a transparent conductive material forming an upper electrode. This strip can be several tens of centimetres wide and several tens of meters long, and can be considered as a single photovoltaic cell of very large dimensions. It must consequently be divided into devices of smaller dimensions in order to be adapted to final applications.
U.S. Pat. No. 5,457,057 discloses a method for manufacturing photovoltaic cells from strips such as those obtained by the method disclosed in U.S. Pat. No. 4,485,125. According to this latter method, the strip is divided for example by being sheared or sawed into individual cells during a first step, the individual cells being then connected in modules including several individual cells via connecting tapes. However, the step of dividing the strip into individual cells involves numerous short-circuiting defects in proximity to the cutting edges of the cells, in particular following accidental contact between the upper electrode and the lower electrode. This method thus requires additional steps for checking and testing each cell after cutting. Such a method does not therefore allow the cells to be used as they are immediately after the cutting step and consequently reduces the efficiency of the method.
In order to overcome this drawback, U.S. Pat. No. 5,457,057 proposes removing the defects resulting from the cutting step during two subsequent steps. A first step consists in insulating, on the individual cut cells, a central active region from the peripheral region including the aforementioned defects resulting from the cutting step. For this purpose, it is proposed to remove the layers of material forming the upper electrode and the semi-conductor materials forming the n-i-p or p-i-n junction along the contour of the cells to expose the substrate. The removal of these layers can be achieved by scribing, chemical etching or using a laser beam. During a second step, the peripheral region including the cutting defects is separated from the central region by being cut from the substrate from the back of the cell in the zone where the layers have been removed. According to an alternative which is also disclosed in this method, the peripheral region is kept and used for making connecting means for the cell.
The removal of the semi-conductor layers forming the junction is particularly difficult since it requires the implementation either of very aggressive chemical products or a difficult method for ablating said layers by laser or scribing which can also cause short-circuits.
Moreover, conservation of the peripheral region results in a cell whose space requirement can be more significant for a given active region. This additional space requirement can constitute a considerable limitation on the use of these cells in certain applications in which they have to be incorporated in objects of small dimensions such as wristwatches and suchlike.
The principal object of the present invention is thus to overcome the drawbacks of the aforementioned prior art by providing a batch manufacturing method for photovoltaic cells wherein a plurality of photovoltaic cells are made in a single batch, this batch being then able to be easily divided into individual cells without any risk of damage to the cells and without any risk of creating short-circuits between the different layers forming each cell.
Therefore, according to a first aspect, the invention concerns a batch manufacturing method for a plurality of individual photovoltaic cells, each cell including:
an electrically conductive substrate forming a first electrode; PA1 a second transparent or semi-transparent electrode and photovoltaic semi-conductor body forming the junction arranged between the first and the second electrode; PA1 (a) providing at least one strip of conductive material, PA1 (b) punching in succession in said strip substrates forming the lower electrodes along a cutting line substantially defining the shape and the dimensions of the desired cells, PA1 (c) replacing the cut substrates in the strip in the locations where they were cut out, PA1 (d) depositing on one of the faces of the strip semi-conductor materials forming at least one n-i-p or p-i-n junction, PA1 (e) depositing a transparent or semi-transparent layer of electrically conductive material on top of said semi-conductor materials to form an upper electrode, and PA1 (f) removing from the strip the cut substrates coated with the semi-conductor materials and the upper electrode to form individual photovoltaic cells. PA1 an electrically conductive substrate forming a first electrode, PA1 a second transparent or semi-transparent electrode and a semi-conductor photovoltaic body disposed between the first and the second electrode, PA1 (a) providing at least one strip of conductive material, PA1 (b) cutting out in succession in said strip substrates which form the lower electrode for each cell and which have the dimensions of the desired cell, so that each of said substrates is connected to the rest of the strip by at least one bridge of material, PA1 (c) depositing semi-conductor materials forming at least one n-i-p or p-i-n junction on one of the faces of the strip, PA1 (d) depositing a transparent or semi-transparent layer of an electrically conductive material on top of said semi-conductor materials to form an upper electrode, except over the bridge or bridges of material, PA1 (e) removing from the strip, by cutting out the bridge or bridges of material at the location which is not coated with said transparent or semi-transparent material, the substrates coated with said semi-conductor materials and the upper electrode to form individual photovoltaic cells.
the method being characterised in that it includes at least the following steps:
The use of the technique consisting in punching substrates having the dimensions of a desired individual cell in a strip of conductive material, then replacing the cut substrates in the strip at the very locations where they were cut out, is a simple, reliable, rapid and consequently particularly economical cutting technique.
Moreover, prior to the removal step, this method allows a series of steps to be performed on the strip for the purpose of forming a plurality of finished photovoltaic cells, including, in particular, the step of transferring markings onto the cells in the event that the latter are intended to form dials for timepieces or suchlike and, if necessary, the deposition of contact pads which facilitates the connection of the individual finished cells.
This method is particularly advantageous compared to methods of the prior art in that the removal of the individual strips from the strip of conductive material is achieved by simple pressure applied to the cells, and thus does not require the use of a laser or water jet cutting device which is complex and expensive to implement. Furthermore, after removal from the strip, the individual cells no longer need to be subjected to subsequent treatment steps, with the exception, if required, of a test step. The method according to the invention thus provides cells which are ready to be used.
According to a second aspect, the invention also concerns a batch manufacturing method for a plurality of individual photovoltaic cells, each cell including:
the method being characterised in that it includes at least the following steps:
As a result of these features, any short-circuiting problem which might result from plastic flow of the upper electrode during the cutting out of the finished individual cells, is avoided since the conductive material has been removed above the bridges of material which are intended to be cut.
In an advantageous manner, it will also be noted that, according to the method of the invention, the cells held on the conductive strip by said bridges of material are electrically insulated from each other. This allows, in particular, the cells to be tested while they are still on the strip and defective cells to be marked. Once marked, the defective cells can be ignored during the subsequent manufacturing steps, such as marking or decorative design transfer steps, in particular when such cells are intended to form dials for timepieces or suchlike.
According to an advantageous feature common to both aspects of the invention, the strip is cut into sections of strip, each including a predetermined number of cells, prior to execution of the step of depositing said semi-conductor materials and the layer of transparent or semi-transparent material.
According to another advantageous feature common to both aspects of the invention, the layer of semi-conductor material is plasma deposited, while the transparent or semi-transparent layer forming the upper electrode is deposited by vapor deposition. It will be noted that this latter method is directional and does not cover or barely covers the flanks perpendicular to the plane of the substrate.
This feature is particularly advantageous in conjunction with the second aspect of the invention. Indeed, plasma deposition of the layer of semi-conductor materials leads to the covering of the external edges and flanks of each substrate forming the lower electrode, so that the substrate is perfectly electrically insulated from the transparent or semi-transparent layer which is subsequently deposited, given the high resistivity of the semi-conductive layers forming the junction. The arrangement of a margin on the periphery of each cell is thus avoided, which allows the active surface of each cell to be increased. This moreover improves the aesthetic appearance of the cell, which is important in the event of the use of such a cell as a timepiece dial.